The present invention relates to a method and device for battery state determination.
A very wide range of methods are known and have been proven in practical use for determination of the state of a battery, in particular of a rechargeable battery (e.g., a lead-acid rechargeable battery which is used as a starter battery in motor vehicles).
By way of example, EP 1 353 190 A1 discloses a method for determination of the wear of an electrochemical storage battery, in which the amounts of charge converted are determined continuously during the storage cycles of the energy store, and a wear variable which characterizes loss of storage capacity is calculated as a function of the determined amount of charge converted. This makes use of the fact that the charging process governs the structural changes which cause the wear in the electrochemically active materials in the energy store, and overcharging, which affects the wear, is also taken into account. The process of continuously determining the amounts of charge converted makes use of the fact that the loss of storage capability increases progressively as the amount of charge converted during the charging cycles increases, and that the discharge cycles have no significant influence on this loss.
Methods are also known for battery state determination, for example, from DE 195 40 827 C2, in which battery-specific families of characteristics of battery aging are used in order to determine a battery aging value, with the aid of the family of characteristics from recorded instantaneous values of the battery aging influencing variables.
By way of example, DE 103 35 928 A1 discloses a method for determination of the state of charge of a characteristic variable which is related to the storage battery, in which a first state of charge value, which is related to the rest voltage of the battery, and a second state of charge value, which is related to the amount of charge converted, are determined. The two state of charge values are evaluated to determine the change in their state of charge, in order to derive a characteristic variable for the battery state from the two state of charge changes.
DE 102 317 00 A1 discloses a method for determination of the amount of charge which can still be drawn from a battery, by measurement of the battery current and voltage values at at least two times before and during a rise phase and during or after a decay phase of a charging or discharge process.
These and other methods for battery state determination are used in vehicles in order to ensure that the battery is currently carrying out its tasks, and will carry out its tasks in the future. A wide range of further functions are built on the information relating to battery state identification and have no visible effects for the driver of the vehicle. For example, loads such as seat heating are switched off when a low state of charge SOC and/or a specific state of health SOH of the battery state identification are/is found. The accuracy and the stability of the results of the battery state identification therefore play an important role. The accuracy of battery state identification can be ensured by means of appropriate algorithms and measurement techniques. The stability of the results must, however, be monitored separately. Output variables from the battery state identification, such as the state of health SOH or the loss of capacity Qv, are based on different input variables, such as the battery terminal current, the battery terminal voltage, the temperature and internal state variables, such as the internal resistance, the battery temperature from a battery temperature model, etc. If a major error occurs for any reason whatsoever in one of the measurement variables, input variables or state variables, this has immediate effects on the output variables. However, it may also frequently be necessary to identify rapid changes in the battery state as such. For example, it may be important to identify a rapid increase in the loss of capacity. In this case, it is then necessary to decide whether this is an actual change in the battery, or a result of normal scatter or spurious values of the measurement, input or state variables.
It would be advantageous to provide an improved method and device for battery state determination.